Typically, a printed circuit board (PCB) contains a plurality of vias, each electrically connecting a conductive trace on one layer of the PCB to one or more conductive traces on one or more other layers of the PCB. Some vias may be interconnected such that a portion of the via is not disposed along a conductive of the PCB. For example, where a via interconnects two internal layers of the PCB, the portion of the via extending from an outermost one of the internal layers to a surface of the PCB is referred to as a via stub. Via stubs serve no useful function in the circuit of the PCB and may cause signal distortion and/or other problems.
Backdrilling is a technique used to remove a via stub. Backdrilling uses controlled depth drilling techniques to remove the undesired conductive plating in the via stub region. Typically, the via stub region is removed using a drill bit larger in diameter than the drill bit that was used to create the original via hole. While such backdrilling may eliminate many of the problems associated with via stubs, the larger drill bit produces a hole larger than the original via which negatively impacts i) the clearance requirements for signal traces for each layer through which the backdrilled hole passes and ii) the minimum via-to-via spacing.